More than one-half of the 6 million pregnancies occurring each year in the U.S. are unplanned. The availability of long-term, efficacious contraception offers the most practical solution to this public health crisis. While implantable or injectable forms of progestin-only steroid contraceptives most nearly meet these requirements, available therapies are associated with high rates of discontinuation due to abnormal bleeding. Abnormal "breakthrough" bleeding (BTB) resulting from increased numbers of easily disrupted endometrial capillaries and venules. This application's central hypothesis is that contraceptive-associated BTB results from: a) reduced endometrial hemostatic potential secondary to decreased expression of perivascular stromal cell tissue factor (TF), the primary initiator of hemostasis; b) a deficient perivascular stromal extracellular matrix (ECM) and increased fibrinolysis stemming from reduced type-I plasminogen activator inhibitor (PAI- 1) expression; and c) enhanced endometrial angiogenic activity producing structurally compromised capillary and venular networks. it is postulated that these pro-hemorrhagic changes result from the induction of a functionally hypoprogestational state due to: l) alterations in the expression of progesterone receptor (PR) isoforms; 2) changes in nuclear factors interacting with these PR isoforms (e.g. jun or cAMP-activated proteins); and/or 3) increases in antiprogestational autocrine factors (e.g. TGFbeta). Three Specific Aims will test this central hypothesis. Specific Aim l will examine endometrial specimens from both cycling women and those using long-term progestin-only contraceptives to determine whether the hemorrhagic state induced by long-term contraceptive therapy is associated with: reduced expression of TF and PAI-1, alteration in the content and/or isoforms of PR and ER, or the variable expression of modifiers of PR- modulated transcription. Specific Aim 2 will evaluate the effects of various synthetic progestins used in a variety of concentrations +/- ethinyl estradiol in both sustained and pulsed exposure regimens, on the expression of TF, PAI-1, PR and ER isoforms in endometrial stromal cells (ESCs) cultured for up to 60 days. These studies will determine the optimal contraceptive steroid composition and/or exposure regimen which enhance expression of endometrial TF, PAI-1 and progestational activity. Specific Aim 3 will expose cultures of highly purified human endometrial endothelial cells (HEECs) to: a) ovarian steroids; b) conditioned media from control and steroid-exposed ESC and glandular cultures; c) co-culture with ESC and gland cells; and d) plasma-derived factors (e.g. thrombin), to determine whether HEEC angiogenesis is modulated by: direct steroid effects mediated by low levels of HEEC ER and PR and/or indirect angiogenic effector(s) or a change in the perivascular ECM. Results of these studies are expected to permit formulation of rational approaches to reduce irregular bleeding associated with steroid contraceptive therapy. Such a reduction would be expected to reduce the occurrence of unplanned pregnancies.